java - 开始新 Activity 时应用程序崩溃

Question

我创建了一个 Activity 来测试一些名为 Parse 的东西。 我已尝试启动它 5 次。我用不同的名称重新创建了 Activity ，重写了 Intent 内容并更改了运行代码的按钮。所有的尝试都失败了。

这是我的代码:

    Intent intent = new Intent(Login.this,Parse.class);
    startActivity(intent);

我得到以下 LogCat:

    11-10 10:26:27.211 17518-17518/? I/art: Late-enabling -Xcheck:jni
    11-10 10:26:27.427 17518-17556/rafaelmarinho.dobau D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
    11-10 10:26:27.441 17518-17518/rafaelmarinho.dobau D/Atlas: Validating map...
    11-10 10:26:27.543 17518-17518/rafaelmarinho.dobau D/AndroidRuntime: Shutting down VM
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime: FATAL EXCEPTION: main
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime: Process: rafaelmarinho.dobau, PID: 17518
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{rafaelmarinho.dobau/rafaelmarinho.dobau.Parse}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.access$800(ActivityThread.java:155)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:135)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5343)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at rafaelmarinho.dobau.Parse.onCreate(Parse.java:12)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:6010)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292)
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.access$800(ActivityThread.java:155) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:135) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5343) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905) 
    11-10 10:26:27.545 17518-17518/rafaelmarinho.dobau E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700) 
    11-10 10:26:29.382 17518-17518/rafaelmarinho.dobau I/Process: Sending signal. PID: 17518 SIG: 9

那么我该如何解决这个问题呢？

Answer 1

每当您尝试禁用主页按钮或在操作栏上执行任何操作时，您都应该检查 getSupportActionbar 是否不为空，因为这取决于应用程序主题。

if(getSupportActionBar()!=null){
setDisplayShowTitleEnabled(false);
}